The present invention relates to a mechanical acceleration sensor for activating a gas generator of an inflator in an air bag system or a pretensioner in a seatbelt system. The present invention also relates to a gas-pressure activating apparatus employing the mechanical acceleration sensor.
Vehicles, for example, automobiles, are provided with an air bag system or a seatbelt system. For an inflator in the air bag system or a pretensioner in the seatbelt system, a gas generator is employed as a means of generating a driving medium for the inflator or the pretensioner. The gas generator is activated by an acceleration sensor which operates on sensing a predetermined level of acceleration. Such acceleration sensors include two types, that is, a sensor that outputs an electric signal, and a mechanical sensor that outputs a mechanical displacement of a member. The former is superior in the acceleration pulse discriminating power and hence advantageous in that an erroneous operation is unlikely to occur. On the other hand, it requires a power supply and electrical connection. Therefore, the installation position is limited. In contrast, the latter acceleration sensor is inferior to the former in the acceleration pulse discriminating power, but it is less costly and needs no electric supply nor electrical connection. Therefore, the latter type of acceleration sensor is advantageous in that it can be used without limitation on the installation position. Under these circumstances, various proposals have heretofore been made with regard to the mechanical sensor.
There is one form of such mechanical sensor in which when a predetermined level of acceleration acts on the vehicle, a firing pin of the sensor is percussively actuated to activate the inflator of the air bag system. This type of mechanical sensor has a weight, a latch lever, and a firing pin, which are movably supported on a sensor casing. The firing pin, which is spring-loaded, is released from the hold by the latch lever by the inertial movement of the weight relative to the casing, thereby allowing the firing pin to perform a percussive action (for example, see Japanese Utility Model Application Laid-Open (KOKAI) No. 2-32464, in which, particularly, the position of the weight relative to the latch lever is adjustable.)
However, the above-described conventional mechanical sensor is originally intended to be applied to an air bag. Therefore, in the conventional mechanical sensor, the acceleration sensing direction, that is, the direction of inertial movement of the weight, is set in only one direction. For example, if this mechanical sensor is used as a means for activating a pretensioner attached to a retractor in a seatbelt system, the set-up posture of the mechanical sensor relative to the retractor must be reversed depending upon whether the retractor is installed on the left-hand side of the right-hand side with respect to the vehicle. The limitation on the set-up posture necessitates preparation of different kinds of mechanical sensor in accordance with the position in which the retractor is installed.
Further, in the conventional mechanical sensor, the weight is movably supported on the casing relatively loosely. Therefore, it is difficult to expect an accurate operation, and the operation is readily influenced by the set-up posture of the sensor. In addition, since the space for the operation of the latch lever and the space for the movement of the weight must be provided separately from each other, the outer shape and overall weight of the sensor become large in comparison to the weight of the weight member.